Chime



July 3, 1951 M. ALEXANDER CHIME Filed Nov. 9, 1945 I INVENTOR. M

MM 61 4, filmmr, W

Patented July 3, 1951 UNITED STATES PATENT OFFICE to Nutone, Incorporated, New York, N. Y., corporation of New York Application November 9, 1945, Serial No. 627,706

3 Claims.

This invention relates to sound producing chime or signal elements of the resonator type. Conventional chimes of this type heretofore available have comprised a vibrataole bar and a resonator placed adjacent the bar and tuned to vibrate at its frequency. The operation of such units is based upon the fact that if a fiat bar of elastic material, such as steel or brass, is supported properly and is given a sharp blow at an appropriate place it will emit a tone of low intensity but of relatively long duration, and that if this bar, appropriately supported, is placed over an opening in a cavity properly tuned to respond or be excited by the vibrations from the bar, then the intensity of the sound is multiplied many fold at the beginning of the vibrations but the tone is of much shorter duration. In either instance the same total energy of the blow is expended but, in the latter case. the tone is of sufficient magnitude to be employed for signal or musical purposes. The bar of such apparatus is said to be resonated and the tuned cavity is said to be the resonator. Heretoiore all resonator type chimes have consisted of the bar, constituting the primary source of the vibrations and the resonator which, in effect, amplifies the sound.

As distinguished from the resonator type of structure chimes also have been available comprising long slender chime tubes suspended by cords. Such tubes produce sound only by their physical vibration; no resonation takes place and, while their tone is pleasant, still they are so awkward in shape that their use has been substantially confined to musical instruments, cathedral clocks and the more conspicuous, ornamental types of signals.

Briefly, this invention is based upon the concept and determination that the cavity within a thin-walled tubular element capable of being vibrated may be employed as a resonator responsive to the vibrations of the tubular element. Otherwise expressed, a self-resonating tubular chime element is provided L1 the form of a thinwalled tube closed at its ends and of such proportions that the cavity within the tube is excited to resonance by the physical vibrations of the tube when the tube is struck. From the commercial point of view the invention is particularly useful because it eliminates the use of separate elements and provides for a more compact arrangement of parts including strikers, either of the mechanical or electromagnetic types.

The design and proportions of the tube are of importance in achieving the self-resonating action. It is requisite that the vibrations from mental openings in the tube ends.

within the tube be permitted to escape therefrom. Therefore, the tube is provided with one or more openings, preferably though not necessarily, in the form of a relatively large opening at the central portion of the tube and, if desirable, supple- It is also necessary that the tube be supported appropriately, for instance at nodal points so that the vibrations are not damped.

From the foregoing discussion of the principles upon which the invention is predicated and the following detailed description of the drawings in which typical embodiments of the invention are disclosed, those skilled in the art readily will comprehend the various modifications to which the invention is susceptible.

In the drawings:

Figure 1 is a side elevation of a chime element or musical device constructed in accordance with this invention.

Figure 2 is a side elevation of the chime tube showing plugs for closing the ends of the tube.

Figure 3 is a sectional view similar to Figure 2, showing enclosure plugs of a diiferent type.

Figure 4 is a view similar to Figure 3, showing another form of end plugs of greater mass and inertia.

Figure 5 is an end view of the end closure of the tube shown in Figure 1.

The chime element shown in Figure 1 is a thinwalled tube l which may be of steel, brass or other suitable material of an elastic, vibratable nature. The tube has end closures 22 and, in this form, has a sound emitting aperture 3 which i may be located approximately midway of the tube ends. The support for the tube is shown, somewhat diagrammatically, in the form of cords or hangers 4-4 which pass through the tube and have their ends suitably attached to hooks or brackets. The tube supporting means may be of conventional type other than the form shown but, inasmuch as this part of the structure forms no part of the present invention, the details are not disclosed. Thus, as understood by those skilled in the art, rubber grommets or other suitable means may be utilized in place of the cords 4 shown. The supports are located preferably at nodal points and are of a yieldable nature so that the energy imparted to the tube when struck may be fully devoted to vibrating it.

The manner in which the tube is distorted when in vibration is, undoubtedly, quite complex, including not only the fundamental (or first harmonic, as the fundamental is sometimes called) but other harmonics and overtones. However,

for purposes of illustration, the tube is shown as being set in fundamental vibration designated by the dot and dash lines when struck a sharp blow from a hammer or striker 5 which may be located at any suitable point, either at the end or, better still, intermediate the supports. Under these circumstances the mid portion of the tube is presumed to vibrate back and forth, the end portions simultaneously swinging back and forth in opposite directions and the nodal points being substantially stationary or free of vibration.

In this tube, the frequency of vibration and the frequency of resonation are coordinated as described, and the physical vibrations corresponding to wall movement, as represented by the dotdash lines, induce a resonant vibration of the air within the cavity. Therefore, sound vibrations which, in effect, are amplified are emitted from the opening 3.

By Way of example a musical device or chime capable of functioning in this manner may be made of a tube of 65-35 brass, 37 centimeters long, 1% inches in diameter, with a wall thickness of .032 inch. The end caps are of similar thickness and each has a hole therein of 1.45 centimeters while the tube has an additional hole, approximately at the center thereof, 1.95 centimeters in diameter. A tube having these dimensions vibrates and resonates at a frequency of 729 cycles per second, corresponding approximately to the second F# above middle C. The nodal points of this tube are 8.4 centimeters from the ends.

I have further discovered that the mass or inertia of the caps at the tube conveniently provide a means of causing the tube to vibrate at given frequencies. This discovery is valuable because it enables frequency of vibration of the tube to be coordinated or related to its frequency of resonation. In other words, the pitch may be changed without substantially changing the volume of the cavity (which is an important factor governing the frequency of resonation of the tuning of the apparatus) or, conversely, the volume may be changed without substantially changing the pitch through the use of caps of different density or unit weight. By virtue of this determination one is enabled to construct two tubes of the same overall length and diameter which vibrate at quite diiferent pitch.

In Figure 2 end caps 65 are provided which are of greater inertia than the thin sheet metal end caps of the tube shown in Figure 1. Such a tube, by way of example, may be approximately 37 centimeters long, of 65-35 brass, 1 inches in diameter, with a wall thickness of .032 inch. The tube may have a hole, approximately at the center thereof, of 1.7 centimeters and at each end a plug is provided 2.43 centimeters in length, each plug having a hole therein of .91 centimeter. This tube vibrates and resonates at 528 cycles per second which is approximately on octave above middle C. The nodal points of this tube are located 5.1 centimeters from each end. It may be observed that this tube, although the same length as the tube previously described having end caps of negligible mass, has a pitch approximately three full tones lower.

A further example of a tube of this sort is as follows: Diameter 1 inches; wall thickness .032 inch; 65-35 brass; length 55.85 centimeters. The tube may have a hole intermediate its length of 1.6 centimeters and plugs at each end having a mass, m, of 57.1 grams, but neither plug has a hole therein. This tube vibrates and resonates at 266 cycles per second, approximately the tone of 4 middle C. The nodes are spaced 9.1 centimeters from the end.

The foregoing examples illustrate various embodiments of the present invention and others, of different sizes, shapes and tones, may be constructed utilizing the following formulae:

For a brass tube 1 inches in diameter with the wall thickness of .032 inch made of -35 brass having a thin plug in each end of negligible mass, the relation is:

where f is the frequency in cycles per second; and L, the overall length in centimeters.

For a brass tube of the same type having plugs in each end which are of substantial mass, m, in grams, the relation between the pitch and frequency is as follows:

](L+5) (1582-0334 logiom) X 10 It is understood at present by those skilled in the art that the opening in a resonator bears a relationship to its frequency of resonation. For instance, as the length of the tube is decreased, or as the mass of the plugs in the tube ends is increased, it is desirable that the aperture C3 from which vibrations are emitted be increased. In tubes quite short in length, an aperture may be required which is unreasonably large in size, so much so as to weaken the tube and prevent it from vibrating properly. In such instances an aperture of suitably small size may be placed in the tube wall and additional passageways for the air within the tube may be provided in the ends of the tube.

Such arrangements are shown, using plugs of different masses, in Figures 3 and 4, respectively. The relation between the masses of the plugs, the length of the plug and the radii of the holes in the plugs may be as follows, using steel as the plug material, with a density of 7.8 grams per cubic centimeter:

m=44.85b-24.54bR

where m is the mass of one plug, in grams; 1), the length of plug in centimeters, and R, the radius of the hole in each plug, in centimeters. The exact location of the nodal points will vary in accordance with tube length and pitch. As a general guide the greater the mass of the end closures of the tube the closer the nodal points will approach the ends of the tube. The nodal points conveniently may be located on a tube of unknown pitch by conventional methods.

In the design of a tube having the same overall diameter, material and wall thickness previously indicated, the following equation is useful in ascertaining that the resonating frequency of the tube cavity be the same as that of the frequency of vibration of the tube.

Where f is the resonating frequency in cycles per second; a, the velocity of sound in air; and V, the net volume inside the tube, that is, its length minus the plug-thickness times the cross sectional inside area, in cubic centimeters.

This equation, calculated upon a velocity of sound in air of 34,432 centimeters at approxi mately 22 C. gives The foregoing equation is independent of the material of which the tube may be constructed.

(03 for tubes of the siz described may be taken as 1.621 centimeters).

It should be clearly recognized that the foregoing equations and examples are intended only to assist those skilled in the art in the construction of self-resonator tubes in accordance with this invention and are not presented by way of limitation, inasmuch as vibration frequencies will vary in accordance with the type of the material of which the tube is constructed, its wall thickness and overall length. Different results entailing appropriate modifications also will be obtained should unsymmetrical plugs be employed or should the holes in the plugs be dissimilar. In the foregoing disclosure the plugs are presumed to be symmetrical and the holes in the plugs are presumed to be circular and identical in size.

From the foregoing principle which have been presented those skilled in the art readily may determine the compensations necessary to accommodate plugs of dissimilar size or plugs having dissimilar apertures therein.

When the frequency of vibration of the vibratable element is exactly equal to the frequency of resonation of the cavity within the element, then the greatest so-called amplification of sound is noticed. Under these circumstances the energy causing the vibration is dissipated and tone diminishes to inaudibility over a period of time sometimes may be undesirably short; for instance, in the utilization of these devices for slight detuning of the resonation cavity with repsect to the frequency of vibration of the vibratable part. However, this detuning should not be so pronounced that resonation fails; in

general, detuning of not more than a half a tone produces the desired result.

Having described my invention, I claim:

1. A musical instrument comprising a symmetrically constructed tubular member having endwise closures and. a sound emitting opening, the said tubular member, when struck, being vibratable throughout its entire length in a fundamental mode of vibration, and the said tubular member being so proportioned that the air in the cavity delineated by the said tubular member is capable of resonating at the same frequency of vibration as that of the tube itself when it is struck.

2. A musical device comprising a symmetrically constructed, thin walled cylinder having endwise closures and at least one aperture leading to the interior of the cylinder, the said cylinder being characterized by vibratability throughout its entire length in a fundamental mode of vibration to produce audible sound when it is struck, the said cylinder also being so proportioned that the air in the cavity delineated by the cylinder, in response to the vibration of the cylinder when it is struck, resonates at the same frequency of vibration as the cylinder.

3. A musical device comprising a symmetrically constructed, thin walled cylinder having endwise closures and at least one aperture leading to the interior of the cylinder, the said cylinder being characterized by vibratability throughout its entire length in a fundamental mode of vibration to produce audible sound when it is struck, the said cylinder also being so proportioned that the air in the cavity delineated by the cylinder, in response to the vibration of the cylinder when it is struck, resonates at the same frequency of vibration as the cylinder, and means for supporting the cylinder at at least one of the nodal points defined by the vibration of the cylinder in the said fundamental mode of Vibration.

LOWELL M. ALEXANDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 485,542 J. Harrington Nov. 1, 1892 656,603 Harrington Aug. 21, 1900 686,301 Jacques Nov. 12, 1901 818,874 Deagan Apr. 24, 1906 890,341 Deagan June 9, 1908 1,100,672 Deagan June 16, 1914 1,595,359 Schluter Aug. 10, 1926 2,133,911 Alexander Oct. 18, 1938 

